A number of medically recognized techniques are utilized for cataractic lens removal based on, for example, phacoemulsification, mechanical cutting or destruction, laser treatments, water jet treatments, and so on.
The phacoemulsification method includes emulsifying, or liquefying, the cataractic lens with an ultrasonically driven needle before the lens is aspirated. A phacoemulsification system 5 known in the art is shown in FIG. 1. The system 5 generally includes a phacoemulsification handpiece 10 coupled to an irrigation source 30 and an aspiration pump 40. The handpiece 10 includes a distal tip 15 (shown within the anterior chamber of the patient's eye 1) that emits ultrasonic energy to emulsify the cataractic lens within the patient's eye 1. The handpiece 10 further includes an irrigation port 25 proximal to the distal tip 15, which is coupled to an irrigation source 30 via an irrigation line 35, and an aspiration port 20 at the distal tip 15, which is coupled to an aspiration pump 40 via an aspiration line 45. Concomitantly with the emulsification, fluid from the irrigation source 30, which is typically an elevated bottle of saline solution, is irrigated into the eye 1 via the irrigation line 35 and the irrigation port 25, and the irrigation fluid and emulsified cataractic lens material are aspirated from the eye 1 by the aspiration pump 40 via the aspiration port 20 and the aspiration line 45.
Turning to FIG. 2, a functional block diagram of a phacoemulsification system 100 known in the art is shown. The system 100 includes a control unit 102 and a handpiece 104 operably coupled together. The control unit 102 generally controls the operating parameters of the handpiece 104, e.g., the rate of aspiration A, rate of irrigation (or flow) F, and power P applied to the needle, and hence the eye E. The control unit 102 generally includes a microprocessor computer 110 which is operably connected to and controls the various other elements of the system 100. The control unit 102 may include an aspiration pump, such as a venturi (or vacuum-based pump) or a variable speed pump 112 (or a flow based or peristaltic pump) for providing a vacuum/aspiration source, which, in the case of a variable speed pump 112, can be controlled by a pump speed controller 116. The unit 102 further includes an ultrasonic power source 114 and an ultrasonic power level controller 118 for controlling the power P applied to the needle of the handpiece 104. A vacuum sensor 120 provides an input to the computer 110 representing the vacuum level on the output side of the pump 112. Venting may be provided by a vent 122. The system 100 may also include a phase detector 124 for providing an input to the computer 100 that represents the phase between a sine wave representation of the voltage applied to the handpiece 104 and the resultant current into the handpiece 104. Further disclosure about the phase detector 124 can be found in U.S. Pat. No. 7,169,123 to Kadziauskas et al., which is incorporated herein in its entirety by reference. The functional representation of the system 100 also includes a system bus 126 to enable the various elements to be operably in communication with each other.
Turning to FIG. 3, the cross-section along the longitudinal axis of a portion of a phacoemulsification handpiece 200 known in the art is shown. Generally, the handpiece 200 includes a needle 210, defining a lumen that is operatively coupled to the aspiration pump 40 (FIG. 1), forming an aspiration line 214. The proximal end of the needle 210 is coupled to a horn 250, which has its proximal end coupled to a set of piezoelectric crystals 280, shown as three rings. The horn 250, crystals 280, and a proximal portion of the needle 210 are enclosed within a handpiece casing 270 having an irrigation port coupled to an irrigation line 290 defining an irrigation pathway 295. The irrigation line 290 is coupled to the irrigation source 30 (FIG. 1). The horn 250 is typically an integrated metal, such as titanium, structure and often includes a rubber O ring 260 around the mid-section, just before the horn 250 tapers to fit with the needle 210 at the horn's 250 distal end. The O ring 260 snugly fits between the horn 250 and the casing 270. The O ring 260 seals the proximal portion of the horn 250 from the irrigation pathway 295. Thus, there is a channel of air defined between the horn 250 and the casing 270. Descriptions of handpieces known in the art are provided in U.S. Pat. No. 6,852,092 (to Kadziauskas et al.) and U.S. Pat. No. 5,843,109 (to Mehta et al.), which are hereby incorporated by reference in their entirety.
In preparation for operation, a sleeve 220 is typically added to the distal end of the handpiece 200, covering the proximal portion of the needle 210 (thus, exposing the distal tip of the needle), and the distal end of the irrigation pathway 295, thereby extending the pathway 295 and defining an irrigation port 222 just before the distal tip of the needle 210. The needle 210 and a portion of the sleeve 220 are then inserted through the cornea of the EYE to reach the cataractic lens.
During operation, the irrigation path 295, the eye's chamber and the aspiration line 214 form a fluidic circuit, where irrigation fluid enters the eye's chamber via the irrigation path 295, and is then aspirated through the aspiration line 214 along with other materials that the surgeon desires to aspirate out, such as the cataractic lens. If, however, the materials, such as the cataractic lens, are too hard and massive to be aspirated through the aspiration line 214, then the distal end of the needle 210 is ultrasonically vibrated and applied to the material to be emulsified into a size and state that can be successfully aspirated.
The needle 210 is ultrasonically vibrated by applying electric power to the piezoelectric crystals 280, which in turn, cause the horn 250 to ultrasonically vibrate, which in turn, ultrasonically vibrates the needle 210. The electric power is defined by a number of parameters, such as signal frequency and amplitude, and if the power is applied in pulses, then the parameters can further include pulse width, shape, size, duty cycle, amplitude, and so on. These parameters are controlled by the control unit 102 and example control of these parameters is described in U.S. Pat. No. 7,169,123 to Kadziauskas et al.
In a traditional phacoemulsification system 100, the applied electric power has a signal frequency that causes the crystal 280, horn 250, and needle 210 assembly to vibrate at a mechanically resonant frequency. This causes the needle 210 to vibrate in the longitudinal direction with a maximum range of motion, which many consider to be the state where the needle's cutting efficacy is at its maximum. However, there are a couple of known drawbacks. First, at this frequency, maximum power is applied to the needle that results in maximum heat introduced into the eye, which can cause undesirable burning of eye tissue. Second, the longitudinal motion can cause the material being emulsified to repel away from the needle, which is undesirable when the goal is to keep the material close to the needle to be aspirated (a quality often referred to as the needle's or handpiece's “followability”).
To address the first issue, the power can be applied in pulses, where little or no power is applied in between the pulses, thus reducing the total amount of power and heat applied to the needle 210. To address the second issue, the power can be applied to the handpiece 200 to cause the needle 210 to vibrate in the transverse direction. An example of this approach is described in U.S. patent application Ser. No. 10/916,675 to Boukhny (U.S. Pub. No. 2006/0036180), which describes causing the needle 210 to vibrate in a torsional or twisting motion, which is a type of transverse motion. This application describes applying to the power to the needle 210 with a signal that alternates between two frequencies, one that causes longitudinal motion, and one that causes torsional motion with a particular type of horn having diagonal slits. This solution does provide for followability, but cutting efficacy leaves much for improvement.
Accordingly, an improved system and method for phacoemulsification is desirable.